Filled soil conditions generally fall along a continuum that can be loosely divided into three categories. At one end of the continuum is the above-mentioned category known as conventional till which generally includes tillage conditions wherein the soil is worked into a garden-like condition before planting. Conventional till is loose and crumbly and has little intact plant residue, sometimes called "trash", present on the surface. A middle category is minimum till wherein the soil is only lightly tilled prior to planting. In minimum till, the soil is firmer and some intact plant residue is present when the next crop is planted. The third category, located at the opposite end of the continuum from conventional till, is no till, wherein the soil remains largely undisturbed after harvest, and the next crop is planted among standing weeds, remaining plant root structure, and other trash. Of the three general categories, conventional till is the oldest and most widely used. However, minimum till and no till, often together called conservation till, are becoming increasingly popular.
It is generally recognized that conservation till provides certain advantages over conventional till, namely, less work, better moisture and nutrient preservation, less chemical loss and redistribution, less erosion and other benefits. These latter advantages are believed due largely to the lesser disruption or working of the soil in conservation till as compared to conventional till and to this end, implement manufacturers have been providing more specialized planting implements and particularly seed and grain drills for planting in conservation till, and particularly no till, which similarly attempt to only minimally disturb the soil, with the intent to preserve these conditions as much as possible. Some of the better known conservation drills, most notably John Deere's 750 Series of no till drills, and drills from Great Plains, Tye, and Crust Buster, provide generally good results in no till and minimum till, particularly when the soil has a hard top crust and is relatively firm and dry. However, in conventional till where several inches of loose soil can be present on the surface of the ground, and in wet soils, such known conservation drills can still form too wide a furrow and disrupt the soil too much, and thus perform less than satisfactorily. Such known conservation drills have been found to be particularly less than satisfactory in river bottom soils including heavy, silty components, known as "gumbo" soils, such as those found in areas such as the Mississippi river valley region of southern Illinois and elsewhere. These soils tend to fracture and fragment easily, thus making difficult to open the soil without breaking it up. Other problem soil include sandy loams which can be extremely fine and almost fluid-like making it difficult to form a narrow, controlled furrow and deposit seed in the bottom of the furrow before it is covered with soil.
A primary reason for generally unsatisfactory performance of the known conservation drills in the above-discussed conditions is the amount of downward pressure that the drills apply against the soil. To cut through trash and open hard, dry no till soil, the conservation drills are heavy, and additionally can apply up to several hundred pounds of downwardly directed hydraulically controlled pressure to each furrow foraging member or opener portion of the planting unit. The hydraulically controlled downward pressure is not necessary in the softer, looser conventional till, and can be switched off. However, just the weight of the units can still provide too much down pressure, resulting in problems such as excessive planting depth which is of critical concern, particularly when planting crops such as soybeans. In wet soils, the heavy drills can even become mired in the soil if conditions are too wet, resulting in delays that can reduce crop yields. To compound the weight problem, pulling the heavier conservation drills, particularly through firm soil, roots and trash, requires relatively large horsepower tractors which are themselves heavy and are known to cause soil compaction problems. Conservation drills and the larger tractors are also costly.
The furrow openers used with the known conservation drills have features that enable them to work well in conservation till, some of which are also good for conventional till, and other features that have been observed to hinder the performance of the drill in the conditions mentioned above. Reference U.S. Pat. No. 4,760,806, which shows one known furrow opener construction. Features of this opener that make it particularly well adapted for conservation till and which are also good for conventional till include a single rotatable furrow forming disk blade offset at a small angle from the direction of travel, and a relatively wide, adjustable gauge wheel located adjacent the side of the disk. which gauge wheel has an axis of rotation located just rearwardly of the disk axis. The gauge wheel is adjustable to precisely control the depth of soil penetration of the disk and also soil displacement on one side of the furrow. The less desirable features include a pivotally mounted seed tube assembly adjacent the opposite or rearwardly facing side of the disk, which seed tube has an extension or boot that extends rearwardly of the seed tube outlet for engaging the adjacent side of the furrow to help form and firm it. A flexible plastic member is provided aft of the seed tube outlet to prevent the seed from bouncing out of the furrow. Additionally, the opener assembly is supported for pivotable movement on a rotatable rockshaft using a draw arm assembly that is steeply oriented and which has a pivot point which is highly placed above to the opener, which is also an undesirable element of the other opener as well.
Limitations observed when using the opener construction of U.S. Pat. No. 4,760,806 in conventional till include the soil displacing or furrow firming characteristics of the seed tube boot which produces a wide furrow in the loose soil, resulting in the above-discussed problems of moisture loss and the like, as well as drag and wear. The flexible plastic member, which is also relatively wide, tends to drag through the furrow and has been observed to even flip seed out of the furrow at times. Additionally, as the seed box empties during operation, the drill becomes lighter, necessitating more steeply orienting the drag arm to place more weight on the openers to compensate for the weight reduction. However, as the drag arm rotates more steeply, because the gauge wheel axis is rearward of the disk axis, and the drag arm pivot point is high above and forward of the disk, the disk and therefore the seed tube and boot are raised slightly relative to the gauge wheel, resulting in seed placement that can be too shallow. On a gradually occurring basis, this can be compensated for to some degree by adjusting the gauge wheel and down pressure to plant deeper. However, on an intermittent basis, such as when planting in bumpy and irregular field surfaces, this problem is not so easily solved and the resulting non-uniform seed depth can significantly affect crop yields. Additionally, the seed tube outlet has been found susceptible to clogging in looser soils at the steeper drag arm angles.
The closer assembly disclosed in U.S. Pat. No. 4,760,806 includes a pair of press wheels mounted on arms pivotally attached to the end of the drag arm in trailing relation to the opener disk, the forwardmost of which press wheels acts to press the seed into the furrow, and the rearward one of which acts to scrub soil over the seed. Shortcomings observed with this closer in conventional till include the shape and orientation of the second wheel tends to cause it to plow in loose soil and drag in wet soil. The second wheel is also made of heavy cast iron and has been observed to bounce significantly at higher pulling speeds. Further, each of the press wheels is adjustably spring biased and requires adjustment or disengagement of the spring for use in conventional till. Although these members can be adjusted to apply no downward spring pressure and even upwardly directed spring pressure, even the weight of the wheels can be too great for some conventional till conditions such as disclosed above. Adjusting the springs can also be a difficult task. In some drills, a dual front and rear rockshaft arrangement is used to achieve narrower row spacing under 10 inches or so. A shortcoming of this arrangement is that adjusting the front openers is a difficult and time consuming task due to the location of the adjusting means under the seed box. Another problem is that the openers are staggered front to rear such that in looser soil, the trailing rear openers tend to push soil over the seed planted by the adjacent leading front openers, resulting in the seed planted by the front gang being covered with too much soil. To compensate for this problem, in some instances the front openers can be set at a shallower depth than the rear openers. However, this does not work in all cases, and in some cases the front openers may have to be locked in an up, non-planting position, which is less productive and for obvious reasons is inconvenient. Still further, in rockshaft arrangements, the lubrication and service points for the front openers tend to be difficult to access.
Further shortcomings of some known conservation drills include a tendency to "walk" as the drill is pulled across a field, that is, the drill tends to rock from end to end, resulting in patches or small areas of a field which are shallowly on non-uniformly planted. Walking has been observed to occur with more frequency as the speed at which the drill is pulled increases, and appears to occur more often in harder soil conditions. Walking is believed to be due largely to the height, weight, and relatively narrow overall width of the drills. Also, in some wet conditions the openers can tend to peel the soil open in continuous solid strips and the closers push the solid soil strips back over the furrow resulting in emergence problems.
The other known conservation drill openers mentioned above differ from that just described in that they utilize a double disk opener construction. That is, these drills all use two rotatable furrow forming disk blades, offset at opposing angles from the direction of travel, for opening the furrow. The furrows opened by these double disk models are typically wider and deeper than the furrows formed by the single disk drill, thus causing more soil displacement and the resulting moisture loss and other soil disruption related problems discussed above.
Drills for conventional till, since the soil is relatively loose and there is little or no intact stuble or crop residue present on the ground, are generally lighter, less rigid, and require less horsepower to pull than the conservation drills discussed above, which are all good features. However, conventional till drills characteristically open a relatively wider, deeper furrow resulting in more soil displacement, deposit the seed in the furrow, and drag some soil over the seed, resulting in the above-named problems. Conventional drills which utilize a double disk opener, in additional to opening a wide furrow, have been observed to leave a small upwardly extending ridge in the center of the furrow that effectively prevents the precise placement of seed at the bottom of the furrow. Some constructions also utilize closing wheels that serve to set planting depth, which has been found to be less preferable than the gauge wheel construction discussed above.